Task assignment in multiagent systems is a complex coordination problem, in particular in systems that are subject to dynamic and changing operating conditions. To enable agents to manage dynamism and change, adaptive task assignment approaches are needed. In this paper, we introduce DynCNET, a protocol for dynamic task assignment that extends standard contract net (CNET). DynCNET allows the agents involved in the protocol to switch the assignment of tasks dynamically. We use an industrial automated transportation system as illustration and present results obtained from a real-world test setting that compare DynCNET with standard CNET and a field-based approach for task assignment.